Sources for deep seismic explorations are very expensive and often not suitable for shallow prospectings for which higher resolutions are required. The most common seismic sources are explosive charges, vibrators, and weight-dropping devices. In near-surface prospectings such as the archaeological one, explosives, although of reduced power, had to be excluded because they do not guarantee a non destructive exploration and require an expensive handling such as security measures, shot-hole drilling and so on. Under many aspects seismic vibrators would represent an adequate means, but their cost is too high. The most simple and economic mechanical devices, usually utilized for shallow prospecting, suffer from several shortcomings; the energy supplied by them is lost in most part, like surface waves and shear waves and is limited to lower frequencies, and the shot repetition rate is too low.
This latter type of source, already experienced at IDAC (G. B. Cannelli, "Geoacoustic Measurement of p-Wave Velocity by Seismic Refraction Technique", Riv. Ital. di Acustica, 8(1), 39-57, 1984), allows only rough prospectings on land.